A PLAN FOR THE STUDY OF THE HYDROGEOLOGY OF BEDROCK OF NEW ENGLAND

By Wayne W. Lapham

U.S. GEOLOGICAL SURVEY

Open-File Report 90-374

Boston, Massachusetts 1990

U.S. DEPARTMENT OF THE INTERIOR

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY

Dallas L. Peck, Director

For additional information, write to:

District ChiefU.S. Geological Survey10 Causeway Street, Suite 926Boston, MA 02222-1040

Copies of this report can be purchased from:

U.S. Geological SurveyBooks and Open-File Reports SectionFederal Center, Bldg. 810Box 25425,Denver, Colorado 80225

CONTENTS

Page

Abstract..................................................................... 1Introduction ................................................................. 2

Background ............................. .". ................................ 2Purpose and scope .......................................................... 2

Regional geology and hydrogeology of bedrock ...................................... 4Geology................................................................... 4Hydrogeology .............................................................. 4

Long-term study objectives ...................................................... 6Proposed plan of initial study ................................................... 8Summary ................................................................... 11Selected references ............................................................ 13

ILLUSTRATIONS

Page

Figure 1. Map showing the six-State New England region .................................. 32. Generalized lithologic map of New England ...................................... 53. Diagram showing objectives for the study of the

hydrogeology of bedrock of New England ....................................... 9

TABLES

Page

Table 1. Summary of well characteristics in bedrock aquifers in New Englandby State .................................................................. 7

2. Hypothetical example of an approach to characterizing the physical frameworkof a rock type in New England ............................................... 12

111

CONVERSION FACTORS AND ABBREVIATIONS

Multiply -By To obtain

foot(ft)

Length

0.3048 meter (m)

gallon per minute (gal/min)

Flow

0.06308 liter per second (L/s)

IV

A Plan for the Study of the Hydrogeology of Bedrock of New England

By Wayne W. Lapham

ABSTRACT

Uses of bedrock in the six-State New England region of Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont are diverse. Bedrock is used as building material, for construction of roads, in many industrial and commercial applica­ tions, as a source of water supply, and as a repository for waste. Although bedrock in New England is an important multiple-use water resource, there has been no coordinated investigation of the hydrogeology of bedrock in the region. There is a critical need for coordinated, systematic, and comprehensive study of all aspects of the hydrogeology of bedrock of New England to aid Federal, State, and local agencies in managing and protecting this valuable water resource.

This report presents a plan for the coordinated, sys­ tematic, and comprehensive study of the hydrogeology of bedrock in New England. Included as part of this plan are brief summaries of previous and current investigations in New England; a summary of the current understanding of the hydrogeology of bedrock on a regional basis; a statement of long-term objectives for study; and a proposed initial study. The initial study is designed to provide a description of the physi­ cal framework of the bedrock needed for subsequent studies that will address the many complex and diverse aspects of the hydrogeology of bedrock of New England.

Several of the most important interrelated objectives required for a comprehensive study of the hydrogeology of bedrock of New England are to (1) characterize the

physical framework of bedrock in relation to scale and to identify factors that control the framework, such as rock lithology, bedding, foliation and geologic stress- strain history; (2) develop methods for identifying and characterizing the areal and vertical distributions of porosity and fractures in bedrock and describe the relation between fracture systems and the hydraulic properties of the rock; (3) describe the occurrence of water and characterize the flow system in bedrock on regional and local scales; (4) determine the sources of water to bedrock wells; (5) develop testing procedures for evaluating the performance of bedrock wells; (6) determine the water-yielding characteristics of bedrock and describe the relation between well yield and factors that affect well yield; (7) describe the background quality of ground water in the bedrock and relate water chemistry to rock chemistry; (8) describe the relation between bedrock ground-water quality and land use; (9) relate the nature of con­ taminant transport in bedrock to the bedrock framework; and (10) determine the nature of the fate and transport of contaminants in the various bedrock types.

These interrelated studies need to be based on a sound understanding, which is presently lacking, of the physical framework of bedrock in New England. Therefore, characterization of this framework is the proposed focus of the initial study.

INTRODUCTION

Background

Uses of bedrock in the six-State New England region of Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont (fig. 1) are diverse. Bedrock is used as building material, for construction of roads, in many industrial and commer­ cial applications, as a source of water supply, and as a repository for waste. These diverse uses generally are incompatible. For example, water withdrawn from bedrock aquifers commonly is used for water supply, but these aquifers commonly are hydraulical- ly connected to areas that contain septic systems, buried storage tanks, road-salt storage piles, landfills, hazardous-waste storage and disposal sites, waste-in­ jection wells, and disposal lagoons. As a result, con­ tamination of water in bedrock aquifers is common, and many domestic, industrial, and municipal wells completed in bedrock have been shut down following degradation of water quality.

Historically, most large municipal water supplies in New England have been derived from stratified-drift aquifers, whereas most domestic supplies have been derived from bedrock aquifers. In recent years, how­ ever, development of industrial and municipal water supplies from bedrock has increased in many areas of New England as demand for water has grown beyond that available from the overlying unconsolidated deposits. The need to locate high-yield wells com­ pleted in bedrock simply, quickly, and economically has increased as demand for water supply has in­ creased relative to available supply. There also is a need to develop methods by which these aquifers can be managed and protected by State and local agencies. One critical aspect of this management and protection is the delineation of recharge areas to wells completed in bedrock.

It is increasingly clear that water in bedrock aquifers is highly vulnerable to contamination from human sources. Under the U.S. Environmental Protection Agency's Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and Resource Conservation and Recovery Act (RCRA) programs and companion State programs, new cases of contamination of water in bedrock aquifers are being discovered continuously. Cleanup of con­ taminated water in bedrock aquifers is costly and extremely difficult, and requires an understanding of

the hydrogeology of the aquifers in the vicinity of the site, which generally is unavailable. This knowledge is based on data describing the physical properties and geologic and hydrologic characteristics of the bedrock, and the geochemical characteristics of water in the bedrock. Physical properties include the frac­ ture characteristics and the primary and secondary porosities of the rock. Geologic characteristics include lithology and geologic history. Hydrologic charac­ teristics include the degree of hydraulic connection between fractures, the rate and direction of ground- water flow, and the rates and locations of recharge and discharge. Geochemical characteristics include back­ ground water quality and the sources and types of chemical constituents in the bedrock.

Crystalline rocks in New England also have been considered as possible deep repositories for the long- term containment and isolation of high-level radioac­ tive waste and spent fuel (U.S. Department of Energy, 1986). Selection of sites for long-term containment of these wastes implies that, beyond a synoptic under­ standing of the hydrogeology of these repositories, there is an understanding of probable long-term chan­ ges in the hydrogeology in the vicinity of the sites and the effects these changes could have on the safe con­ tainment of these wastes. Given the current state of knowledge of hydrogeology of bedrock in New England, and other factors, such as climatic change, it is questionable to predict these long-term changes or their effect on the safe containment of wastes.

Although bedrock of New England is a multiple-use resource and some of the uses are incompatible, and, although bedrock is an important water resource, there has been no coordinated investigation of the hydrogeology of bedrock in the region. Consequently, the hydrogeology of bedrock of New England remains poorly understood. There is a critical need for coor­ dinated, systematic, and comprehensive study of all aspects of the hydrogeology of bedrock of New England to aid Federal, State, and local agencies in managing and protecting this valuable water resource.

Purpose and scope

This report presents a general plan for the coor­ dinated, systematic, and comprehensive study of the hydrogeology of bedrock of New England. Included are brief summaries of previous and current inves­ tigations in New England; a summary of the current understanding of the hydrogeology of bedrock of New England; a statement of long-term objectives for the

73

45°

42°

50 MILES

50 KILOMETERS

Figure 1.-The six-State New England Region.

study of the region's bedrock hydrogeology; and a proposed initial study. The initial study is designed to provide a description of the physical framework of the bedrock needed for subsequent studies that will address the many complex and diverse aspects of the hydrogeology of bedrock of New England.

REGIONAL GEOLOGY ANDHYDROGEOLOGY OF

BEDROCK

Geology

Bedrock in New England is composed of crystalline igneous, crystalline metamorphic, and sedimentary rocks (fig. 2). There has been extensive mapping of bedrock units and interpretation of the structural and geologic history of the region (Billings, 1955; Doll and others, 1961; Goldsmith, 1964; Hussey and others, 1967; Thompson and Norton, 1968; White, 1968; Quinn, 1971; Kane and others, 1972; Zen, 1972; Weed and others, 1974; Cameron and Naylor, 1976; Har- wood and Zietz, 1976; Osberg, Hussey, and Boone, 1985; Hatch, 1988; among others). From a regional hydrogeologic perspective, bedrock in New England can be divided into Proterozoic and Paleozoic igneous and metamorphic rocks; partly metamorphosed lower Paleozoic sedimentary rocks; Cambrian and Or- dovician sedimentary carbonate rocks; and upper Paleozoic, Triassic, Jurassic, and Cretaceous sedimentary rocks.

Proterozoic and Paleozoic igneous and metamorphic rocks are the most widespread in New England. These rocks cover large areas of Maine, New Hampshire, Rhode Island, Vermont, Connecticut, and nearly all of Massachusetts except the Connecticut Valley, Nantucket, and possibly Martha's Vineyard. The most common crystalline igneous rocks are granite, rhyolite, diabase, pegmatite, and basalt (Sin- nott, 1982). The most common metamorphic rocks are gneiss, schist, phyllite, slate, marble, quartzite, and argillite.

Lower Paleozoic metasedimentary rocks, including quartzitic conglomerate, slate, phyllite, argillite, and marble, occur throughout Maine, in several areas in New Hampshire, and in western and southeastern Massachusetts, Rhode Island and Connecticut (Sin- nott, 1982).

Cambrian and Ordovician sedimentary carbonate rocks, consisting largely of limestone, dolomite, and calcareous shale, and some metamorphosed sedimen­ tary carbonate rocks consisting largely of marble, underlie western Vermont and the Housatonic River valley in western Massachusetts and Connecticut. Triassic and Jurassic sedimentary sandstone, con­ glomerate, and shale underlie the Connecticut Valley lowland in west-central Massachusetts and central Connecticut and the Aroostook valley in northern Maine along the border between the United States and Canada. Carboniferous conglomerate, sandstone, siltstone, and shale with some coal under­ lie the Boston and Narragansett basins of eastern and southeastern Massachusetts and southeastern Rhode Island. Igneous and metamorphic rocks underlie Cape Cod. Nantucket Island and Martha's Vineyard are underlain by partly indurated Tertiary coastal plain sediments, which overlie basalt of Triassic or Jurassic age at Nantucket.

Hydrogeology

Although the geology of bedrock in New England has been studied extensively and is reasonably well un­ derstood, there has been no comprehensive com­ panion study of the hydrogeology of bedrock of New England. Most previous investigations of the hydrogeology of bedrock of New England (Ellis, 1909; Cushman and others, 1953; Heald, 1956; Stewart, 1965?; Hodges, 1968; Frimpter and Maevsky, 1979; Sinnott, 1982; Emery and Cook, 1984; Hoag, 1985; Paillet, 1985a; Caswell, 1987; Randall, 1988; among others) have focused on bedrock as an aquifer and, therefore, as a source of water for supply; therefore, the following discussion of the regional hydrogeology of bedrock of New England is from the supply perspec­ tive.

General relations between average well yield and rock type have been determined in New England. How­ ever, these relations may or may not apply at par­ ticular sites. The same rock unit can exhibit substantial areal and vertical variation in hydraulic characteristics, depending on the areal and vertical variation in primary and secondary permeability of the rock, and, therefore, large variation in yield. Con­ versely, rock units that are different lithologically can have similar hydrologic characteristics because of similar fracture characteristics, and, therefore, similar yields.

73

45°

42°

MESOZCXC,PALEOZOIC. AND

MIDDLE PROTEROZOIC

EXPLANATION

COASTAL PLAIN SEDIMENTS

LARGELY SANDSTONE. SHALE, AND CONGLOMERATE

LARGELY CALC-SILICATE METASEDIMENTARY ROCKS

LARGELY DOLOMITE. LIMESTONE. AND SHALE

LARGELY SHALE AND GRAYWACKE

J I 1 LARGELY METASEDIMENTARY 11 I AND METAVOLCANIC ROCKS

[mm ALKALIC AND CALC- 1 ALKALIC GRANITIC ROCKS

50 KILOMETERS

Figure 2.~Distribution of major types of bedrock in New England (Modified from Denny, 1982)

Wells in igneous rocks (granite, rhyolite, diabase, pegmatite and basalt) and metamorphic rocks (gneiss, schist, phyllite, slate, marble, quartzite and argillite) in New England derive nearly all their water from secondary permeability resulting from fractures in the rock (Sinnott, 1982). Similarly, wells in less in­ tensely metamorphosed zones of quartzite, slate, phyllite, argillite and marble derive ground water from fractures in the vicinity of the well. Water to wells from the Cambrian and Ordovician carbonate limestone, dolomite, and calcareous shale is also derived from fractures. Some wells in these carbonate rocks are highly productive, particularly where solu­ tion along fractures has enlarged the openings and created zones of high secondary permeability. Water from wells from the Triassic, Jurassic, and Cretaceous sandstones, conglomerates, and shales is derived from interconnected pores (primary permeability) in the rock matrix, from faults and joints, and from fractures along bedding planes (secondary permeability).

Yields of bedrock wells in New England range from a fraction of a gallon per minute (gal/min) to more than 1,000 gal/min (Hodges, 1968; Cushman and others, 1953; U.S. Geological Survey, 1984). Cushman and others (1953) determined that the yield of a bedrock well in New England depends primarily on four fac­ tors: the number of fractures intersected by the well, the water-bearing capacity of the fractures, the ability of the fractures to transmit water, and the rate of recharge to bedrock in the vicinity of the well. Yields can be high where wells intersect major faults and in areas where the bedrock is overlain by saturated stratified drift (U.S. Geological Survey, 1984). Cush­ man and others (1953) summarized the yields from 1,952 wells from 7 rock types. Results of this sum­ mary indicated that wells in limestone produced the highest average yield, 177 gal/min, and that wells in gneiss produced the lowest average yield, 9.0 gal/min. Between these two extremes, the average well yield was 37.7 gal/min in granite, 32.7 gal/min in Car­ boniferous sedimentary rocks, 19.8 gal/min in Triassic sedimentary rocks, 11.7 gal/min in granite gneiss, and 10.3 gal/min in schist. Cushman and others (1953) also concluded that the topographic setting of the well is related to yield. Wells located in valleys had an average yield of 91.9 gal/min, and wells located on plains, slopes, and hills had average yields of 57.5, 18.8, and 7.7 gal/min, respectively. Average yield may be a poor index for evaluating well yield, however, because a few very high yielding wells can have a significant effect on the average.

Sinnott (1982) and the U.S. Geological Survey (1984) provide recent summaries of bedrock characteristics in New England with respect to well yield. The U.S. Geological Survey (1984) reports that well depths generally range from 100 to 300 ft in sedimentary rock aquifers, and from 20 to 800 ft in noncarbonate crys­ talline and carbonate rock aquifers (table 1). The range of yields is from 1 to 100 gal/min from the sedimentary rock aquifers, from 1 to 25 gal/min from the noncarbonate crystalline rock aquifers, and from 1 to 50 gal/min from the carbonate rock aquifers.

LONG-TERM STUDY OBJECTIVES

A thorough understanding of the hydrogeology of bedrock in the region requires a number of studies. Each of these studies would focus on a specific aspect of the hydrogeology of bedrock; therefore, each study will have different objectives and scope from the other studies. All are interrelated, however, and studies will be best conducted concurrently. Most of these studies need to be based on a sound understanding, presently lacking, of the physical framework of bedrock in New England. For example, all of the States in New England are faced with the problem of ground-water contamination in bedrock a problem that requires immediate and intensive study. How­ ever, the first step in the study of the fate and transport of contaminants in bedrock at a site is to understand the physical framework of the rock in the vicinity of the site and the relation between the framework and the hydraulic properties of the bedrock. For this reason, a study that focuses on the physical framework of the bedrock is viewed as a necessary first step toward understanding the fate and transport of contaminants in bedrock. Therefore, characterization of this framework is the proposed focus of the initial study.

Over the long term, concurrent studies of the hydrogeology of bedrock of New England should be designed to:

(1) Characterize the physical framework ofbedrock in relation to scale and identify fac­ tors which control the framework, such as rock lithology, bedding, foliation and geologic stress-strain history.

(2) Develop methods for identifying and charac­ terizing the areal and vertical distributions of

Table I, Summary of well characteristics in bedrock aquifers in New England by State. [From U.S. Greological Survey, 1985; , no information; ft, feet; gal/min, gallons per minute]

Bedrock aquifer State Well characteristics

Depth (ft)

Sedimentary

Crystalline (noncarbonate)

Carbonate

Conn.

Maine

Mass.

New Hampshire

Rhode Island

Vermont

Conn.

Maine

Mass.

New Hampshire

Rhode Island

Vermont

Conn.

Maine

Mass.

New Hampshire

Rhode Island

Vermont

Common range

100-300

~

100-250

~

100-300

~

100-300

20-800

100-400

100-600

100-300

100-600

100-300

20-800

100-300

~

~

100-300

May exceed

500

~

500

~

500

500

~

1,000

800

500

800

500

~

1,000

~

~

500

Yield (gal/min)

Common range

2-50

~

10-100

~

1-20

~

1-25

2-10

1-20

1-10

1-20

1-10

1-50

10-30

1-50

~

~

5-20

May exceed

500

-

500

~

50

~

200

500

300

100

50

100

200

600

1,000

~

~

300

porosity and fractures in bedrock and describe the relation between fracture sys­ tems and the hydraulic properties of the rock.

(3) Describe the occurrence of water and charac­ terize the flow system in bedrock on regional and local scales.

(4) Determine the sources of water to bedrock wells.

(5) Develop testing procedures for evaluating the performance of bedrock wells.

(6) Determine the water-yielding characteristics of bedrock and describe the relations among well yield and factors that affect well yield.

(7) Describe the background quality of water in the bedrock and relate water chemistry to rock chemistry.

(8 Describe the relations among bedrock ground- water quality and land use.

(9) Relate the nature of contaminant transport in bedrock to the physical framework of the bedrock.

(10) Determine the nature of the fate and transport of contaminants in the various types of bedrock.

A diagram that summarizes these objectives is shown in figure 3.

Investigations that partly address several of these objectives currently are ongoing in New England. These investigations include a study of the hydrogeologic characteristics of fractured rock near Mirror Lake, Thornton, New Hampshire (Paillet, 1985a) as part of the U.S. Geological Survey's Nation­ al Research Program; development of surface- geophysical methods to detect bedrock fractures (F.P. Haeni, U.S. Geological Survey, oral commun., 1989); studies of the hydraulic characteristics of fractured rock, ground-water flow and the fate and transport of contaminants in bedrock as part of remedial inves­ tigations at Superfund sites; a study of the occurrence of water in bedrock by the Massachusetts Office of the U.S. Geological Survey (B.P. Hansen, U.S. Geological Survey, oral commun., 1989); and several State programs of bedrock data collection, compilation and analysis. Fracture-trace analysis and surface geophysics currently is being applied by some firms in

the water-well industry to locate the most likely loca­ tions for high-yield bedrock wells.

Accurate and standardized reporting of data describ­ ing physical, geologic and hydraulic characteristics of bedrock collected throughout the six New England States, the storage of these data in common data bases, and the ability to easily retrieve, manipulate, and display these data are critical for a regional ap­ proach to the investigation of the hydrogeology of bedrock. These data include the locations of test holes and wells, lithologic and water yield logs, pumping rates and time-drawdown data from aquifer tests and other hydraulic tests, borehole- and surface-geophysi­ cal surveys, lineament and fracture-trace analyses, and chemical analyses of water, from bedrock. Cur­ rently, the methods by which these data are collected, reported, stored, and retrieved in State data bases differ in content and accuracy from State to State. Therefore, one important first step toward the regional study of hydrogeology of bedrock of New England is to establish and maintain standardized State bedrock data bases or one New England-wide data base. Utilization of a Geographic Information System (GIS) for data storage-and-retrieval system is one possible approach for management of these data.

PROPOSED PLAN OF INITIAL STUDY

Achieving a thorough understanding of the hydrogeol­ ogy of bedrock of New England will require a number of studies designed to address the several interrelated objectives discussed in the section "Long-term objec­ tives". The first of these objectives is to characterize the physical framework of bedrock in New England. The proposed initial study will provide a description of the physical framework of bedrock in New England at regional and local scales and relate that framework to factors that control the framework, such as rock lithology and geologic history. Characterization of the framework will provide fundamental information necessary for subsequent investigations of water supply, the fate and transport of contaminants, and remediation of contaminated ground water in bedrock systems.

A rock unit can have substantial areal and vertical variation in hydraulic characteristics, depending on the areal and vertical variation in primary and secon­ dary porosity and permeability of the rock. Converse­ ly, rock units with differing lithologies may have

8

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similar hydraulic characteristics because of similar porosity characteristics. Therefore, knowledge of the brittle deformation and resulting fracture charac­ teristics of bedrock (the physical framework of the bedrock) is fundamental information required for studies of the occurrence of water, yields of water from bedrock wells, and the fate and transport of con­ taminants in bedrock aquifers. Characterization of the bedrock framework consists of a description of the following physical properties of the rock: (1) the primary porosity of the rock; (2) the types of rock fracture systems (joints, faults, shear zones) that con­ tribute to the rock's secondary porosity; and (3) the characteristics of these fracture systems, including the areal and vertical geometry, orientation, size of openings, spacing, density, and fracture interconnec­ tion. Fracture systems are the physical features of brittle deformation of rock in response to stress. An understanding of the stress-strain relationships is a key to transfer of fracture system patterns from one geographic area and from one lithologic terrane to another. A large body of knowledge of rock mechanics already exists in the literature and structural geology studies provide a strong foundation for development of hydrologic analysis of secondary bedrock porosity and permeability.

Hydraulic properties of the rock, such as the primary and secondary permeability, storage coefficient, and degree of heterogeneity and anisotropy, are related to the physical properties. The central problem as­ sociated with the characterization of flow and transport in fractured rock is one of heterogeneity and scale (Shapiro and Hsieh, U.S. Geological Survey, written commun., 1989). Characterization of the physical framework of the rock unit or units under investigation at a specified scale provides direct infor­ mation on this heterogeneity and indirect information on the hydraulic properties. For example, charac­ terization of the framework at a regional scale may indicate that flow in the rock on a regional scale can be described using porous-media models, whereas characteristics of the framework on a local scale may indicate that flow in the rock on a local scale only can be described with models that simulate flow in dis­ crete fractures that are separated by solid rock. The characterization of the framework at different scales, therefore, will direct the focus of future studies. As­ sessment of bedrock as a regional water supply probably will require characterization of the physical framework of bedrock on a regional scale, whereas determination of the fate and transport of con­ taminants in bedrock probably will require charac­ terization of the physical framework on a local scale.

Characterization of the physical framework of bedrock at different scales, therefore, is fundamental information required for studies of issues related to water supply and ground-water contamination and is the proposed focus of the initial study.

The primary objective of the initial study is to charac­ terize the physical framework of bedrock in New England at a regional scale, and, where possible, at a local scale, and to relate that framework to controlling factors, such as lithology, bedding, foliation and geologic stress-strain history. A secondary objective is to relate this framework to the hydraulic properties of the rock.

The physical framework of the bedrock will be charac­ terized at regional and local scales by describing the primary porosity of the rock, identifying the types of fracture systems (joints, faults, bedding-plane frac­ tures, shear zones), and the physical characteristics of the fractures (areal and vertical geometry, orienta­ tion, size of openings, spacing, density, and intercon­ nection). This physical framework then will be related to factors that might affect or control these properties. Comparison of the characteristics of the physical framework among sites with similar controls, such as rock type or stress history, will provide infor­ mation on the transferability of these frameworks to other areas of New England where data are not avail­ able. Available hydrogeologic data, such as the primary and secondary permeability, heterogeneity, anisotropy, and storage capacity of bedrock, will be related to this physical framework.

The framework on a regional scale will be charac­ terized using available data, aerial-photograph and/or satelite-imagery interpretation, and field investiga­ tions. It is anticipated that a large body of data already exists that indirectly describes the framework. These data have been collected during studies of the geology of New England, particularly studies of structural geology. Other data from geophysical and hydrologic studies also may be avail­ able. Therefore, the first phase of the study will be a comprehensive review of the geologic, geophysical, and hydrologic literature, and interpretation of data that describe the nature of gross rock porosity (primary, secondary, or both) and the physical char­ acteristics of fractures (the areal and vertical geometry, size of openings, spacing, and fracture den­ sity). Much of the data available will describe the physical framework indirectly because these data were collected for other reasons. For example, struc­ tural mapping of a rock unit commonly includes rose

10

diagrams and stereo plots of measurements of the strike and dip and other characteristics of major joints and faults. Data on these characteristics of fractures, such as strike and dip, lengths, widths, degree of surface weathering, and spacings of these fractures will provide important information describing the brittle deformation of the rock. Available data may be sufficient that a significant part of the study will be spent reviewing and reinterpreting these data. Addi­ tionally, aerial-photograph and/or satelite-imagery interpretation may aid the characterization of the framework on a regional basis. Field investigation also may further refine and verify the in-office char­ acterization of the framework. Field investigations include measurements of surface-fracture charac­ teristics on exposed rock surfaces, measurements of fracture characteristics at outcrops, road cuts, and quarries, and surface-geophysical surveys. Contrac- tural services for mapping fracture systems using aerial-photograph and/or satelite-imagery interpreta­ tion, and for characterization of the framework is possible.

The physical framework will be characterized on a local scale using existing data and on-site field inves­ tigation. Existing data from wells completed in bedrock, such as those collected during remedial in­ vestigations at Superfund sites are available for analysis and interpretation. These data include borehole-geophysical surveys of boreholes completed in bedrock to delineate the vertical distributions of fractures, and surface-geophysical surveys to map areal fracture patterns. Some borehole-geophysical surveys in recently drilled domestic and municipal bedrock wells also may be run. These wells usually are available only for a brief time after completion of drilling pumps are installed in the bedrock wells drilled for water supply soon after completion of drill­ ing. In addition, bedrock test holes at Superfund sites are commonly left as open holes for only a short time after completion of drilling and water-quality sam­ pling, to prevent cross contamination of ground-water caused by vertical flow in the borehole. Geophysical logging of these boreholes soon after completion of drilling will provide information on the size and ver­ tical distribution of fractures in the boreholes.

Extensive, detailed characterization of the framework on a local scale is beyond the scope of this study. Detailed characterization on a local scale requires long-term access to boreholes completed in bedrock for borehole-geophysical logging, aquifer and slug tests using packers, and cross-hole pumping and tracer tests. With the constraint of long-term access to

boreholes, the best approach for study of the bedrock framework at a local scale is the establishment of fractured-rock field research sites. These sites should be located in a variety of fractured rock environments with different degrees of fracturing and complexity, that are identified as important hydrogeologic ter- ranes for water supply or disposal of waste. Installa­ tion, instrumentation, and detailed investigation of fractured-rock field-research sites is expensive and manpower intensive. Also, until understanding of the physical framework of bedrock in New England is improved, selection of sites for detailed study of small- scale bedrock hydrogeology that are representative of large areas of the Region would be difficult.

Some data on the bedrock framework at a local scale currently is being collected and can be included in this study. One site is located near Mirror Lake, West Thorton, New Hampshire. Comparisons of results of studies at Mirror Lake and at other sites in future studies ultimately are expected to enable charac­ terization of local frameworks in different rock lithologies in New England and provide evidence for or against transferability of these results to other sites where data are not available.

An example of how the physical framework of the bedrock might be characterized at regional and local scales and how the framework will be related to fac­ tors that might affect or control these properties, such as rock lithology and geologic history, is illustrated in table 2 (R. Melvin, U.S. Geological Survey, written commun., 1989).

SUMMARY

Uses of bedrock in the six-State New England region of Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont are diverse. Water is commonly withdrawn from bedrock for water supply, but bedrock is commonly hydraulically con­ nected to areas that contain septic systems, buried storage tanks, road-salt storage piles, landfills, haz­ ardous-waste storage and disposal sites, waste-injec­ tion wells, and disposal lagoons. Although bedrock in New England is an important multiple-use water resource, there has been no coordinated investigation of the hydrogeology of bedrock in the region. Conse­ quently, the hydrogeology of bedrock of New England remains poorly understood. There is a critical need for coordinated, systematic, and comprehensive study of all aspects of the hydrogeology of bedrock of New

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Table 2.-Hypothetical example of an approach to characterizing the physical frameworkof a rock type in New England.

I. ROCKLITHOLOGY

Granite

A. SUMMARY OF GENERAL HYDROGEOLOGIC CHARACTERISTICS

No primary porosity.Significant secondary porosity.Fractures are concentrated in discrete zones in the upper 100 meters.Jointing between fractures is irregular.Areal fracture density is highly variable (cite range).Vertical fracture density is highly variable (cite range)

1. HYDROGEOLOGIC CHARACTERISTICS ON A REGIONAL SCALE

a. Shallow joint sets orientation spacingareal fracture density vertical fracture density etc.

b. Deep joint sets orientation spacingareal fracture density vertical fracture density etc.

2. HYDROGEOLOGIC CHARACTERISTICS ON A LOCAL SCALE

a. Shallow joint sets orientation spacingareal fracture density vertical fracture density etc.

b. Deep joint sets orientation spacingareal fracture density vertical fracture density etc.

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England to aid Federal, State, and local agencies in managing and protecting this valuable water resource.

This report presents a general plan for the coor­ dinated, systematic, and comprehensive study of the hydrogeology of bedrock in New England. Included are brief summaries of previous and current inves­ tigations in New England; a summary of the current understanding of the hydrogeology of bedrock of New England; a statement of long-term objectives for the study of the region's bedrock hydrogeology; and a proposed initial study. The initial study is designed to provide a description of the physical framework of the bedrock needed for subsequent studies that will address the many complex and diverse aspects of the hydrogeology of bedrock of New England.

Achieving a thorough understanding of the hydrogeol­ ogy of bedrock in the region will require a number of studies. Each of these studies should focus on a specific aspect of the hydrogeology, and, therefore, each study will have different objectives and scope from the other studies. All are interrelated, however, and studies will be best conducted concurrently. These concurrent studies should be designed to (1) characterize the physical framework of bedrock of New England in relation to scale and identify factors that control the framework, such as rock lithology and geologic history; (2) develop methods for identifying and characterizing the areal and vertical distributions of porosity and fractures in bedrock and describe the relation between fracture systems and the hydraulic properties of the rock; (3) describe the occurrence of water and characterize the flow system in the bedrock on regional and local scales; (4) determine the sources of water to bedrock wells; (5) develop testing proce­ dures for evaluating the performance of bedrock wells; (6) determine the water-yielding characteristics of bedrock and describe the relation between well yield and factors that affect well yield; (7) describe the background quality of ground water in the bedrock and relate water chemistry to rock chemistry; (8) describe the relation between bedrock ground-water quality and land use; (9) relate the nature of con­ taminant transport in bedrock to the bedrock framework; and (10) determine the nature of the fate and transport of contaminants in the various bedrock types.

Most of these interrelated studies need to be based on a sound understanding, which is presently lacking, of the physical framework of bedrock in New England.

Therefore, the characterization of this framework is the proposed focus of the initial study.

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